Reduced vibration tube bundle support device

ABSTRACT

A tube bundle for a shell and tube type heat exchanger has a support system that allows simple fabrication and provides a secure support of the tubes to mitigate vibration and problems associated with vibration. The tube bundle is composed of tubes that are supported by spaced cages having support rods sized to allow ample clearance with the adjacent tubes and configured in alternating positions and alternating orientations so that sets of four widely spaced cages form a complete support network. To ensure secure support to avoid vibration, sets of support stakes are inserted adjacent to (or in between) the cages to bias the tubes against the support rods of the cages. By this, fabrication is simplified, but a secure support system is maintained.

FIELD OF THE INVENTION

This invention relates to tube bundle devices such as heat exchangers,condensers and similar fluid-handling equipment with collections oftubes or rod-like elements, for example, in devices such as nuclearreactors, electrical heaters, or any collection of parallel cylindricalshapes that has a fluid flow passing over the tubes or other elements.

BACKGROUND OF THE INVENTION

Tube bundle equipment such as shell and tube heat exchangers and similaritems of fluid handling devices such as flow dampers and flowstraighteners utilize tubes organized in bundles to conduct the fluidsthrough the equipment. In such tube bundles, there is typically fluidflow both through the inside of the tubes and across the outside of thetubes. The configuration of the tubes in the bundle is set by thetubesheets into which the tubes are set. One common configuration forthe tubes is a rectangular or square formation with the tubes set inaligned rows with tube lanes (the straight paths between the tubes)between each pair or rows, aligned orthogonally to one another. In thisformation, each tube is adjacent to eight other tubes except at theperiphery of the tube bundle and is directly opposite a correspondingtube across the tube lane separating its row from the two adjacent rows.In a triangular tube formation, the tubes in alternate rows are alignedwith one another so that each tube is adjacent to six other tubes (thetwo adjacent tubes in the same row and four tubes in the two adjacentrows).

Increases in throughput in existing exchangers are often desired eitherto reduce capital cost by reducing equipment size or to increaseproductivity factors. A common limiting factor experienced whenevaluating the increase of rates in an exchanger is the potential forflow-induced vibration damage of the tubes. Fluid flow patterns aroundthe tubes may give rise to flow-induced vibrations of an organized orrandom oscillatory nature in the tube bundle.

In the case of devices such as heat exchangers in which heat transfertakes place between the tubes and the surrounding fluid, the changes inthe temperature and density of the fluid as it circulates and flowsaround the tubes may increase the likelihood of vibration. If thesevibrations reach certain critical amplitudes, damage to the bundle mayresult. Tube vibration problems may be exacerbated if heat exchangeequipment is re-tubed with tubes made of a different material than theoriginal tubes, for example, if relatively stiff materials are replacedwith lighter weight tubes. Flow-induced vibration may also occur whenequipment is put to more severe operating demands, for example, whenother existing equipment is upgraded and a previously satisfactory heatexchanger, under new conditions, becomes subject to flow-inducedvibrations. Vibration may even be encountered under certain conditionswhen a heat exchanger is still in the flow stream but without heattransfer taking place, as well as in other tube bundle devices withcollections of rods or rod-like elements in a flow stream with orwithout heat transfer.

Vibration damage is a very expensive event for most situations in anoperating plant. While a heat exchanger may have thousands of tubes,failure of a single tube could lead to shutdown of a process unit, thuscausing substantial economic loss. Thus, reducing or eliminatingvibration is a very desirable goal. Another advantage of minimizing therisk of vibration is to allow the use of axial shellside flow incircuits with gas compressors since compressor power consumption can bedecreased drastically leading to substantial savings in energy costs.

A number of different equipment designs have evolved to deal with theproblem of tube vibration. One example is the rod baffle design. Rodbaffle heat exchangers are shell and tube type heat exchangers utilizingrod baffles to support the tubes and secure them against vibrations.Additionally, rod baffles can be used to reduce shell-side flowmaldistribution and to create a more uniform shell-side flow. The term“rod baffle” refers to the annular rings, placed every 15 cm or so alongthe length of the tube bundle, in which the ends of a plurality ofsupport rods are connected to form a cage-like tube support structure.

Rod baffle exchangers, however, tend to be approximately 20 to 40% moreexpensive than conventional shell-and-tube exchangers. Moreover, therehave been situations where tube bundle devices of this kind have failedowing to flow-induced vibrations. A significant problem with rod bafflesis the difficulty in loading the tubes between the rods. In order toprovide a secure support and minimize vibration, the spacing betweenrods is very close to the diameter of the tube. In some arrangements,the diameter of the rod is approximately the same size of the lanebetween tubes. This requires very careful threading of the tubes throughthe cages and greatly increases the difficulty and time involved ininstallation. Rod baffle heat exchangers are described, for example, inU.S. Pat. Nos. 4,342,360; 5,388,638; 5,553,665; 5,642,778.

As explained in U.S. Pat. No. 5,553,665, certain applications of the rodbaffle design such as surface condensers and power plant applicationsmay benefit from longitudinal-flow, with shell-side pressure losses tobe minimized. Reduction in shell-side pressure losses may beaccomplished by increasing rod baffle spacing, thereby reducing thenumber of rod baffles, or by decreasing the number of tubes byincreasing the tube pitch dimension, i.e., the distance between twoadjacent rows of tubes as measured from the center of the tubes.Increasing baffle spacing is usually not an attractive option, sinceincreased baffle spacing increases the likelihood of flow-induced tubevibration occurrence. Decreasing the tube count by increasing tube pitchdimension produces decreased shell-side pressure loss forlongitudinal-flow between rod baffles, but requires oversized supportrod diameters, leading to increased rod baffle pressure losses, whichmay offset any decrease in longitudinal-flow, shell-side pressure lossresulting from the reduced tube count. This would also lead to a moreexpensive exchanger owing to the increased shell diameter for aspecified tube count. The rod baffle design described in U.S. Pat. No.5,553,665 represents an attempt to deal with the pressure drop problemsof the rod baffle configuration. Another example of a design intended toavoid a significant increase in the longitudinal-flow, shell-sidepressure loss is described in U.S. Pat. No. 5,642,778.

Alternative designs are the “Eggcrate” and “Square One” designs. These,however, can be even more expensive than the rod baffle design, and theydo not eliminate tube chatter that could lead to tube failure. Chatteris the motion of a tube hitting the tube supports because of the gapbetween the support and the tube outside diameter. The gap is requiredto allow for inserting the tubes through the eggcrate or square onesupport when the bundle is being constructed. From economic andoperational viewpoints, therefore, the rod baffle design represents amore hopeful starting point.

Besides good equipment design, other measures may also be taken toreduce tube vibration. Tube support devices, or tube stakes as thesesupport devices are commonly known (and referred to in thisspecification), may be installed in the tube bundle in order to controlflow-induced vibration and to prevent excessive movement of the tubes. Anumber of tube supports or tube stakes have been proposed and arecommercially available. U.S. Pat. No. 4,648,442 (Williams), U.S. Pat.No. 4,919,199 (Hahn), U.S. Pat. No. 5,213,155 (Hahn) and U.S. Pat. No.6,401,803 (Hahn), for example, describe different types of tube stakesor tube supports which can be inserted into the tube bundle to reducevibration. Improved tube stakes are shown in U.S. Pat. No. 7,032,655 andU.S. Publication No. 2005/0279487, both to Wanni et al., and thecontents of which are incorporated herein by reference.

A tube bundle device, which is believed to be more effective, morereliable, easier to fabricate and less expensive than a conventionalheat exchanger of the rod baffle type, has been developed and isdisclosed in U.S. Pat. No. 7,073,575 and U.S. Pat. No. 7,219,718, thecontents of which are incorporated herein by reference. In that device,a tube support cage similar to a rod baffle is placed at extendedlocations along the length of the tubes, e.g. every 50-200 cm apart, andin most cases about every 60-150 cm, thereby making fabrication of sucha tube bundle much easier and less expensive, as compared toconventional rod-baffle devices, in which the rod-baffle supports aretypically placed no more than approximately 15 cm apart. The tubes aresupported by rods or flat bars in each tube lane at the cage locations,compared to the cages provided in every other tube lane in the rodbaffle design. The tube bundle is stiffened by inserting tube stakesbetween the tube support cages, preferably at the midpoint of the tubespan between the cages. While this system is effective, it would bedesirable to provide an alternate design that can be produced withsimple fabrication while still ensuring vibration mitigation.

SUMMARY OF THE INVENTION

Aspects of the invention are directed to a tube bundle device comprisingtubes arranged parallel to one another and defining a tube bundle with alongitudinal axis, wherein the tubes are arranged in rows and columnswith an x-tube lane separating adjacent rows and a y-tube laneseparating adjacent columns. The tube bundle device comprises a firsttube support cage comprising a baffle frame with a plurality of paralleltube support members secured to the baffle frame in a planesubstantially perpendicular to the longitudinal axis, each tube supportmember extending in a first orientation in alternating x-tube lanes, asecond tube support cage comprising a baffle frame with a plurality ofparallel tube support members secured to the baffle frame in a planesubstantially perpendicular to the longitudinal axis, each tube supportmember extending in a second orientation at an angle to the firstorientation in alternating y-tube lanes, a third tube support cagecomprising a baffle frame with a plurality of parallel tube supportmembers secured to the baffle frame in a plane substantiallyperpendicular to the longitudinal axis, each tube support memberextending in the first orientation in alternating x-tube lanes that areoffset by one lane from the first tube support cage, and a fourth tubesupport cage comprising a baffle frame with a plurality of parallel tubesupport members secured to the baffle frame in a plane substantiallyperpendicular to the longitudinal axis, each tube support memberextending in the second orientation in alternating y-tube lanes that areoffset by one lane from the second tube support cage. At least one setof tube support stakes is inserted in the tube bundle adjacent to andspaced from one of the tube support cages substantially parallel to andoffset in alternating lanes from at least some of the tube supportmembers of the adjacent tube support cage. The first, second, third andfourth tube support cages form a set that together defines a grid oftube support members disposed in each x-tube lane and each y-tube lane.The tube support members have a thickness that is between 80-98% of thewidth of an x-tube lane or a y-tube lane, thus defining free spacebetween each tube and an adjacent tube support member. The tube supportstakes bias the tubes against adjacent tube support members.

A set of tube support stakes can be disposed adjacent to each tubesupport cage. A set of tube support stake can be disposed betweenadjacent tube support cages in the set.

Aspects of the invention are also directed to a tube bundle devicecomprising tubes arranged parallel to one another and defining a tubebundle with a longitudinal axis, wherein the tubes are arranged in rowsand columns with an x-tube lane separating adjacent rows and a y-tubelane separating adjacent columns. The device further comprises a firsttube support cage comprising a baffle frame with a plurality of paralleltube support members secured to the baffle frame in a planesubstantially perpendicular to the longitudinal axis, each tube supportmember extending in a first orientation in alternating x-tube lanes, anda first set of tube support stakes inserted in the tube bundle adjacentto and spaced from the first tube support cage substantially parallel toand offset from at least some of the tube support members. A second tubesupport cage comprises a baffle frame with a plurality of parallel tubesupport members secured to the baffle frame in a plane substantiallyperpendicular to the longitudinal axis, each tube support memberextending in a second orientation at an angle to the first orientationin alternating y-tube lanes, and a second set of tube support stakes isinserted in the tube bundle adjacent to and spaced from the second tubesupport cage substantially parallel to and offset from at least some ofthe tube support members. A third tube support cage comprises a baffleframe with a plurality of parallel tube support members secured to thebaffle frame in a plane substantially perpendicular to the longitudinalaxis, each tube support member extending in the first orientation inalternating x-tube lanes that are offset by one lane from the first tubesupport cage, and a third set of tube support stakes is inserted in thetube bundle adjacent to and spaced from the third tube support cagesubstantially parallel to and offset from at least some of the tubesupport members. A fourth tube support cage comprises a baffle framewith a plurality of parallel tube support members secured to the baffleframe in a plane substantially perpendicular to the longitudinal axis,each tube support member extending in the second orientation inalternating y-tube lanes that are offset by one lane from the secondtube support cage, and a fourth set of tube support stakes is insertedin the tube bundle adjacent to and spaced from the fourth tube supportcage substantially parallel to and offset from at least some of the tubesupport members. The first, second, third and fourth tube support cagesform a set that together defines a grid of tube support members disposedin each x-tube lane and each y-tube lane. Each tube support cage isspaced apart at least a distance of 300 mm measured along thelongitudinal axis. The tube support stakes bias the tubes againstadjacent tube support members thereby stiffening the tubes to resistflow-induced vibration potential.

Additional tube support stakes may be provided adjacent the entrance andexit of the tube bundle to provide additional support for the tubes inthese regions. The tube support stakes can have a plurality of spaceddimples and corrugations.

The invention is additionally directed to a heat exchanger having a tubebundle for transporting fluids for heat exchange comprising tubesarranged parallel to one another and defining a tube bundle with alongitudinal axis, wherein the tubes are arranged in rows and columnswith an x-tube lane separating adjacent rows and a y-tube laneseparating adjacent columns. The tube bundle includes a set of four tubesupport cages. Each tube support cage comprises a baffle frame with aplurality of parallel tube support bars secured to the baffle frame in aplane substantially perpendicular to the longitudinal axis. The set offour tube support cages are axially spaced along the longitudinal axissuch that the tube support bars of two tube support cages extend in afirst orientation in alternating x-tube lanes and the tube support barsof the other two tube support cages extend in a second orientation at anangle to the first orientation in alternating y-tube lanes. At least oneset of tube support stakes is inserted in the tube bundle adjacent toand spaced from at least one of the tube support cages substantiallyparallel to and offset from at least some of the tube support members ofthe adjacent tube support cage in a woven configuration. The tubesupport stakes are formed with seats to support the tubes. The set offour tube support cages together define a grid of tube support barsdisposed in each x-tube lane and each y-tube lane, and each tube supportcage is spaced apart from another tube support cage in the set at leasta distance of 300 mm measured along the longitudinal axis. The tubesupport bars have a thickness that is at most 98% of the width of anx-tube lane or a y-tube lane, thus defining free space between each tubeand an adjacent tube support bar. The tube support stakes support thetubes in the seats and bias the tubes against adjacent tube supportbars.

These and other aspects of the invention will become apparent in view ofthe following detailed description, especially when taken with thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic of a tube bundle with the tubessupported by tube support cages and tube stakes according to theinvention showing enlarged details of the tube support cages and thetube stakes;

FIG. 2 is an enlarged view of a tube stake for use with the tube bundleof FIG. 1;

FIG. 3 is an enlarged view of another tube stake for use with the tubebundle of FIG. 1;

FIG. 4 is a side perspective view of a conventional rod baffle bundle;and

FIG. 5 is a simplified schematic of a variation of the tube bundle ofFIG. 1 having additional tube stakes at the end portions of the tubebundle.

Like elements in the drawings are designated with the same referencenumerals.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In this specification and claims, the terms “vertical” and “horizontal”are used in the relative sense with respect to the orientations of theelements of the tube support cages and of the stakes, that is, todesignate a relative orientation of the support cage elements or of thestakes with respect to one another and the axis of the device. Thus,references to the “vertical” orientation mean that the orientation isorthogonal to a specified “horizontal” orientation, without implyingthat the orientations are true vertical or true horizontal. This appliesespecially when the axis of the heat exchanger itself is vertical orhorizontal, so that all the support cages and stakes will be at truehorizontal. Thus, the references to “vertical” and “horizontal” inrelation to the orientation of the elements of the tube support cagesand of the stakes are to be taken on the assumption that thelongitudinal axis of the tube bundle device is itself true horizontaland that the specified orientations are relative to one another nottrue. For example, in a heat exchanger with a true horizontallongitudinal axis, the elements of the tube support cages may be atangles of 45° to the true horizontal/vertical but still be “vertical”and “horizontal” with respect to each other. In a heat exchanger with avertical longitudinal axis, all the elements of all the tube supportcages will be at true horizontal but are nevertheless to be consideredto be “vertical” and “horizontal” if their orientations relative to oneanother about the longitudinal axis are orthogonal.

This invention is explained with reference to a shell and tube type heatexchanger in which a bundle of heat exchanger tubes is secured betweentubesheets within a shell and liquid is directed through and around thetubes to effect heat exchange. This type of tube bundle could be used ina heat exchanger as described or in a condenser, nuclear fuel rod deviceor any other type of ordered arrangement of parallel tubes with fluidflowing over them. For convenience and brevity the invention will bedescribed with reference to the device as a heat exchanger althoughother tube (or rod) bundle devices may also be constructed according thepresent principles. The tube bundle will be fitted into the surroundingshell in a conventional manner, for example, with two fixed tubesheetsif the exchanger is to operate with only a small temperaturedifferential or, more commonly, with one stationary tubesheet and onefloating tubesheet, or with a U-tube bundle having only one (stationary)tubesheet.

FIG. 4 shows a conventional heat exchange tube bundle 100 that uses arod baffle support system. The bundle 100 is composed of a plurality ofelongated heat exchanger tubes 102 disposed in parallel and secured ateach end by tubesheets 104, as is known. The tubes 102 are spaced fromeach other by tube lanes. Disposed along the length of the heatexchanger tubes 102 are a plurality of rod baffles 106 about every 150mm. Each rod baffle 106 is formed as an annular ring 108 that supportsthe ends of support rods 110 that extend across the ring 108. As seen,the support rods 110 extend transversely across the bundle in the lanesbetween the tubes 102. By this arrangement, vibrations induced by theflow of liquid through the bundle can be reduced. In this system, thesize tolerance of each support rod 110 must be carefully designed. Toclosely support the tubes 102, only a small clearance is provided toload the tubes 102 in place through the baffle 106, which causesdifficult loading and increases fabrication costs. However, undersizingthe rods 110 to provide easier tube loading causes the bundle to losethe ability to avoid vibration damage, particularly at the shell inletand outlet.

FIG. 1 shows a tube bundle 10 that is designed to address theseproblems. As will be explained below, the tube bundle 10 is designed toaccommodate a greater throughput and be smaller than existingexchangers. These conditions lead to higher velocities experienced inthe tube bundle and can lead to greater tendency for vibration.

The tube bundle 10 comprises a number of parallel tubes 12 in arectangular configuration, that is, with rows 14 of tubes 12 and columns15 of tubes 12 extending in two directions with x-tube and y-tube lanes16 defined between the tube rows 14 and tube columns 15, respectively.As seen in the figures, only several rows, columns and lanes are labeledfor purposes of simplicity, but it should be understood that thesereference numerals are intended to refer to each row, column and lane,respectively. The tubes 12 are connected to the tubesheets 18, 20 ateach end of the tube bundle in a conventional manner. The tubesheets 18,20, in turn, will be installed into the shell of the exchanger. Ofcourse, other configurations of the tubes 12 within the bundle 10 arepossible, including for example a triangular configuration. The lanespace 16 would need to be adjusted accordingly to fit the tube supportmembers 26.

The tubes 12 are supported by tube support cages 22 that are disposed atintervals along the length of the tubes 12. The tube support cages 22are of four different types that repeat throughout the bundle anddesignated in the drawings as A, B, C and D. Each tube support cage 22is formed of a ring 24 or plate baffle with a central cut-out window. Aplurality of tube support members or rods 26 extend across the centralopen area and are secured at their ends to the ring 24. The cages 22 canbe prefabricated for more efficient and less expensive assembly.

The rods 26 can be any configuration, but are preferably in the form offlat bars welded to the baffle. Of course, the rods 26 may be any shape,including circular, rectangular, or square cross-section, and referredto herein as “rods” for convenience and brevity regardless of theircross-sectional shape. The rods 26 may be directly welded to the sidesof the ring 24 (across its wall thickness) or, with a more complicatedconstruction, received in recesses or apertures in the annular ring 24,shaped appropriately to the cross-section of the rods formed by drillingwith the rods secured in the recesses or apertures by welding, brazingor other securing expedients.

The thickness of the rods 26 is preferably undersized in relation to thetube lanes 16. To provide ample clearance around the rods 26 forinsertion of the tubes 12, the thickness of the rods can be 98% of thewidth of the lane, preferably in a range of 90% to 98%. In the case ofthe rods 26 configured as flat bars, the thickness refers to the widthof the bar. For example, the rods 26 may be about 95% as wide as thetube lane 16. In particular, if a tube lane measured as the spacingbetween two adjacent tubes is 6.35 mm, the rod is sized with a thicknessof 6.0 to 6.2 mm. This allows the tubes 12 to be readily inserted intothe prefabricated cages 22, which makes bundle loading a fairly easytask. On large diameter bundles, small rods may be deflected by flow andfor this reason, it may be desirable to use flat bars as the rods 26 fora greater modulus, resulting in greater axial strength. It is alsocontemplated that several crossbars may be used to stiffen the primarybars. The absence of complete support from the rods 26 does not,however, diminish the effectiveness of the overall support systembecause additional support is provided by the tube stakes which areinserted into the tube bundle, as explained below.

As noted above, there are four different configurations of cages 22. Thefour types A, B, C, D are seen in FIG. 1 extending from left to rightacross the bottom of the figure. The different configurations relate tothe orientation of the cage 22 when installed in the bundle 10. Theterms “horizontal” and “vertical” used herein are used for descriptivepurposes to indicate relative position between adjacent elements. Itshould be appreciated that the entire assembly could be turned thuschanging the orientation, while the relative orientations betweenelements will remain the same.

As seen, the first type, A, has horizontally disposed rods 26 that beginat the bottom portion of the ring 24 and are spaced to be disposed inx-tube lanes 16 between alternate horizontal rows 14. The second type,B, has vertically disposed rods 26 that begin at the left portion of thering 24 and are spaced to be disposed in y-tube lanes 16 betweenalternate vertical columns 15. The third type, C, has horizontallydisposed rods 26 that begin at the top portion of the ring 24 and arespaced to be disposed in x-tube lanes 16 between alternate horizontalrows 14. The fourth type, D, has vertically disposed rods 26 that beginat the right portion of the ring 24 and are spaced to be disposed iny-tube lanes 16 between alternate vertical columns 15. So, each cage 22has rods 26 that are oriented in only one direction. By this, each setof four cages 22 of the types A, B, C, D will provide a rod 26 in everylane 16 between each row 14 and each column 15 of tubes 12 fullysupporting the bundle.

Each tube support cage 22 is positioned at a spaced interval along thelength of the bundle 10. In this arrangement, the spacing is wider thanconventional support cages, for example at least 300 mm between cages22. The spacing can be as much as 600 mm (for 19.05 mm diameter tubes)and 1200 mm (for 25.4 mm diameter tubes) between cages 22. If desired,the distance between support cages/stakes may be increased in the middleportion of the exchanger because the axial velocity in the middleportion of the bundle 10 is parallel to the tubes and therefore is lesslikely to cause vibration. The cages 22 are secured to each other, asseen for example in FIG. 4, by tie bars or tie rods 112.

Due to the decreased size of the rods 26, the use of fewer cages 22 andthe alternate arrangement of rods 26, loading of the tubes 12 throughthe cages 22 can be easily accomplished. After the tubes 12 are loaded,additional anti-vibration support is provided by the insertion of tubesupport stakes 30 to stiffen the tubes 12 disposed in the bundle.

Referring to the top row in FIG. 1, four different configurations ofanti-vibration (AV) tube support stakes 30 are shown from left to rightas AV-A, AV-B, AV-C, and AV-D. The tube support stakes 30 at eachlocation are disposed in the same direction and are disposed in a lanebetween alternate rows or columns. Configuration AV-A utilizes two tubesupport stakes 30 that are both disposed horizontally and are disposedin a lane 16 between two adjacent rows 14 that is offset from the lane16 in which the rod 26 of the adjacent cage 22 is positioned. This canbe appreciated by comparing the configuration of the A cage 22 with theAV-A stake configuration in FIG. 1.

Similarly, configuration AV-A utilizes two tube support stakes 30 thatare disposed vertically in a lane 16 between columns 15 beginning at theleft portion of the bundle. Configuration AV-B utilizes two tube supportstakes 30 that are disposed horizontally in a lane 16 between rows 14beginning at the top portion of the bundle. Configuration AV-D utilizestwo tube support stakes 30 that are disposed vertically in a lane 16between columns 15 beginning at the right portion of the bundle. Similarto the cages 22, by this configuration each set of the fourconfigurations provide a tube support stake 30 in every x-tube andy-tube lane 16 between the rows 14 and columns 15, respectively. Ofcourse, if the bundle is composed of more tubes 12, more rods 26 andmore tube support stakes 30 would be used at each position. As long asthe rods 26 and corresponding tube support stakes 30 are disposed inalternating lanes 16, each row 14 and each column 15 will be fullysupported. All of the tube support stakes 30 may be tied together ateach location, for example, by circumferentially wrapped braided cablesand/or clamps.

As seen in FIG. 1, the locations of the cages 22 and tube support stakes30 also alternate. Each adjacent cage 22 type and tube support stake 30configuration is oriented in the same manner. For example, cage type Ahas horizontally oriented rods 26 that are disposed in alternate lanesas the horizontally oriented tube support stakes 30 of configurationAV-A. This is true for each adjacent, matched pair: B and AV-B; C andAV-C; D and AV-D.

In the rectangular tube arrangement, the alternating vertical/horizontaldisposition of the support rods 26 will result in the tube supportstakes 30 in each set being parallel to the support rods 26 of one ofthe adjacent cages 22 so that the tubes 12 are held by the supportstakes 30 firmly against the support rods 26 to which they are parallel.In the triangular tube arrangement, it is preferable for the orientationof the support stakes 30 at a given location to be parallel to thesupport rods 26 of one of the adjacent cages 22 in order to hold thetubes firmly against the rods 26 of that cage 22. Of course, in atriangular arrangement, the spacing between the tubes will increaseslightly and the alternate orientation of the cages and stakes may be atan angle that is not 90 degrees. So, the shape created by the rods andstakes in each set may be a rhombus rather than a square.

The alternating configuration provides a benefit in terms of permittingfreer fluid flow through the bundle. The parallel alignment of the tubesupport stakes 30 with the support rods 26 of an adjacent cage 22 andoffset configuration has the effect of urging every tube 12 against asupport rod 26 or stake 30 to give the final bundle the rigidity itrequires for satisfactory operation. The insertion of the tube supportstakes 30 into the tube bundle forces the tubes 12 away from the surfaceof the support stakes 30 and biases them toward the rods 26. The effectis similar to a woven basket. In this way, the tubes 12 are slightly (upto 2 mm) deflected so as to provide tube support not only at the tubesupport stake locations but also at the tube support cage stations aswell.

It is noted that no tube supports stakes are provided at thelongitudinal center of the bundle between the two sets of cages becausethe tube support stakes 30 are not needed at every span between cages22. This is especially true near the mid-region(s) between the inlet andoutlet nozzles because the shell flow is mostly axial and has a verysmall tendency to cause vibration damage. It is possible to dispensewith the tube support stakes 30 at other positions, as well, dependingon the particular bundle configuration and vibration analysis. Theparticular design will be application specific.

A variation of the present invention is illustrated in FIG. 5. In thisvariation, the tube bundle 50 includes additional tube support stakes 30located at AV-A′ and AV-AD′ in order to provide additional bundlestiffening of the tubes at the entrance and exit regions of the bundleto ensure that all of the tubes of the bundle are well supported. It iscontemplated that in the event the tube bundle has a U-bendconfiguration (i.e., entrance and exit regions on are the same side ofthe bundle) then additional tube support stakes would only need to beprovided at one location (i.e., AV-A′ or AV-AD′).

The tube support stakes 30 can have any configuration provided that theyare dimensioned to impart the increased tube separation on insertioninto the tube bundle to hold the tubes firmly against the support rodsof the cages. Thus, for example, the tube stakes described in U.S. Pat.No. 4,648,442 (Williams), U.S. Pat. No. 4,919,199 (Hahn), U.S. Pat. No.5,213,155 (Hahn) and U.S. Pat. No. 6,401,803 (Hahn) might be usedprovided that their dimensions are satisfactory to the purpose. Thepreferred type of tube stake is, however, the type shown in U.S. Pat.No. 7,032,655 (Wanni et al.), to which reference is made for adescription of these preferred tube stakes, which are called dimple tubesupports. Another preferred form of tube stake which may be used in thesame manner is described in U.S. Pub. No. 2005/0279487, to whichreference is made for a description of these preferred tube stakes,which are called saddle tube supports. A combination of these types mayalso be used. Full details of these types of supports are disclosed inthe above patent and application, which have been incorporated herein,along with this type of support arrangement from U.S. Pat. No.7,073,575, which has also been incorporated herein.

Referring to FIG. 2, a dimple tube support stake 40 is shown disposed ina lane between tubes 12. The dimple tube support stake 40 is formed as astake or strip 42 having an elongated body with a series of raisedportions, corrugations or dimples 44 that are spaced to form a seat foreach adjacent tube 12. FIG. 3 shows a saddle tube support 50 formed as astake 52 formed of two sheets 54 of stiff material, each with an opposedraised section 56 or corrugation having a rounded central cup 58 thatforms a seat for each adjacent tube 12. Of course, differentconfigurations and methods of forming the seats are possible. Theseconfigurations provide easy insertion while reliably locking the tubesin place. They are also economical to fabricate.

In these types of tube supports or stakes, the corrugations that facethe tubes function to deflect the tubes slightly to provide resilientsupport for the tubes while, at the same time, enabling the supportstakes to be readily inserted into the bundle. At its outer extremity,each tube support stake has dimples which deflect the tubes slightly inthe same way but which lock more securely onto the outermost tubes so asto minimize the likelihood of undesirable dislocation of the tubesupport stakes during handling or in operation. The present invention isnot intended to be used in connection with tube supports having dimplesand/or corrugations. It is contemplated that other support devices maybe used within the tube lanes to force or bias the tubes against therods.

If desired, bypass shrouds can be provided at the top and bottom of tubebundle 10 to preclude longitudinal bypassing of the shellside fluid.These shrouds are known and are formed with a flat face that sitsagainst the outermost tubes and a peripheral flange at each end. Theflange is a chordal segment of a circle of diameter matching theinternal diameter of the exchanger shell so that when the tube bundle isinserted into the shell, the flange conforms closely to the interior ofthe shell to preclude entry of shell side fluid into the shroudedregion. The shrouds may be made in standard lengths and a number of themmay be bolted (or otherwise fastened together end-to-end) through theflanges so as to extend over the tubes in all areas except at the inletand outlet ends where flow to the shell inlet and outlet is required.The shrouds are fastened to the tube support cages for adequaterigidity, for example, by having the flanges bolted together with a tubesupport cage in between them.

In a triangular tube arrangement, a similar disposition of the tubesupport cages and tube support stake sets can be made, but in this case,the alignment of the support rods in the cages at each successive axiallocation is rotated by a multiple of 60° so that the original alignmentis restored at the fourth location (i.e. the support rods aresuccessively aligned at 0°, 60°, 120° and so on), with the stakesinserted in a similar alignment pattern. Given the desirability ofhaving the tubes support stakes inserted parallel to the support rods ofan adjacent support cage, a typical mode of insertion would be with therelative angular positions of the cage support rods and tube supportstakes indicated at angular displacements of 0°, 60°, 120° relative tothe first cage. In a triangular tube arrangement, the spacing betweentubes 12 may be increased slightly over the conventional arrangement toaccommodate the cage support rods.

During assembly, the tubes 12 are inserted through the cages 22 and intoone or both tubesheets 18, 20. In the case of a tube bundle withU-shaped tubes received in one tubesheet, the cages 22 will be put ontothe free ends of the tubes 12 and the tubes 12 then secured in thesingle tubesheet. In the case of a bundle with two tubesheets, the tubes12 will normally be passed through the cages 22 and into one or bothtubesheets, following which, the tubes 12 will be secured to one or bothof the tubesheets, according to exchanger design, e.g. by welding orwith an expanded joint.

The preceding description explains an arrangement in which the pitch andtube dimension are constant, but it will be recognized by those ofordinary skill in the art that assembly disclosed herein can beconstructed to operate on rows of tubes having a variable pitch orvariable tube dimensions. For example, the spacing or curvature of theseats of the tube supports could be easily modified. Moreover, those ofordinary skill in the art will recognize that various changes andmodifications can be made to the arrangement herein and remain withinthe scope of the invention as defined in the appended claims.

1. A tube bundle device, comprising: tubes arranged parallel to oneanother and defining a tube bundle with a longitudinal axis, wherein thetubes are arranged in rows and columns with an x-tube lane separatingadjacent rows and a y-tube lane separating adjacent columns; a firsttube support cage comprising a baffle frame with a plurality of paralleltube support members secured to the baffle frame in a planesubstantially perpendicular to the longitudinal axis, each tube supportmember extending in a first orientation in alternating x-tube lanes; asecond tube support cage comprising a baffle frame with a plurality ofparallel tube support members secured to the baffle frame in a planesubstantially perpendicular to the longitudinal axis, each tube supportmember extending in a second orientation at an angle to the firstorientation in alternating y-tube lanes; a third tube support cagecomprising a baffle frame with a plurality of parallel tube supportmembers secured to the baffle frame in a plane substantiallyperpendicular to the longitudinal axis, each tube support memberextending in the first orientation in alternating x-tube lanes that areoffset by one lane from the first tube support cage; a fourth tubesupport cage comprising a baffle frame with a plurality of parallel tubesupport members secured to the baffle frame in a plane substantiallyperpendicular to the longitudinal axis, each tube support memberextending in the second orientation in alternating y-tube lanes that areoffset by one lane from the second tube support cage; and at least oneset of tube support stakes inserted in the tube bundle adjacent to andspaced from one of the tube support cages substantially parallel to andoffset in alternating lanes from at least some of the tube supportmembers of the adjacent tube support cage, wherein the first, second,third and fourth tube support cages form a set that together defines agrid of tube support members disposed in each x-tube lane and eachy-tube lane, wherein the tube support members have a thickness that isbetween 90-98% of the width of an x-tube lane or a y-tube lane, thusdefining free space between each tube and an adjacent tube supportmember, and wherein the tube support stakes bias the tubes againstadjacent tube support members.
 2. The tube bundle device of claim 1,wherein each tube support cage is about 95% the width of an x-tube laneor a y-tube lane.
 3. The tube bundle device of claim 1, wherein eachtube support cage is spaced apart at least a distance between 300 mmmeasured along the longitudinal axis.
 4. The tube bundle device of claim1, wherein each tube has a diameter in a range of 12-22 mm and each tubesupport cage is spaced apart a distance of about 500-700 mm measuredalong the longitudinal axis.
 5. The tube bundle device of claim 4,wherein each tube has a diameter of approximately 19 mm and each tubesupport cage is spaced apart a distance of about 600 mm.
 6. The tubebundle device of claim 1, wherein each tube has a diameter in a range of23-40 mm and each tube support cage is spaced apart a distance of about1100-1300 mm.
 7. The tube bundle device of claim 6, wherein each tubehas a diameter of about 25.4 mm and each tube support cage is spacedapart a distance of about 1200 mm.
 8. The tube bundle device of claim 1,wherein there is a set of tube support stakes disposed adjacent to eachtube support cage.
 9. The tube bundle device of claim 1, wherein thereis a set of tube support stake disposed between adjacent tube supportcages in the set.
 10. The tube bundle device of claim 1, wherein thetube support stakes have a plurality of spaced projections, theprojections forming a seat for an adjacent tube.
 11. The tube bundledevice according to claim 10, wherein the spaced projections are one ofspaced dimples and spaced corrugations.
 12. The tube bundle device ofclaim 1, wherein the tube support stakes have a plurality of spacedsaddles, each saddle forming a seat for an adjacent tube.
 13. The tubebundle device of claim 1, wherein some of the tube support stakes have aplurality of spaced dimples and some of the tube support stakes have aplurality of spaced saddles, wherein the pairs of dimples and saddlesform seats for adjacent tubes.
 14. The tube bundle device of claim 1,wherein at least some of the tube support stakes have a combination ofdimples and saddles that form a seat for an adjacent tube.
 15. The tubebundle device of claim 1, wherein each tube support member is a flatbar.
 16. The tube bundle device of claim 1, wherein each baffle frame isformed of a plate with a central cut-out window.
 17. The tube bundledevice of claim 1, wherein the tube bundle has a square cross section.18. The tube bundle device of claim 1, wherein the tube bundle has atriangular cross section.
 19. The tube bundle device of claim 1, furthercomprising a shell and a tubesheet connected to the shell that supportsthe tube bundle.
 20. The tube bundle device of claim 1, wherein the tubebundle having a first end forming an entrance region and a second endforming an exit region, wherein the tube bundle device furthercomprising at least one additional tube support stake inserted into thetube bundle adjacent one of the first end and the second end.
 21. A tubebundle device, comprising: tubes arranged parallel to one another anddefining a tube bundle with a longitudinal axis, wherein the tubes arearranged in rows and columns with an x-tube lane separating adjacentrows and a y-tube lane separating adjacent columns; a first tube supportcage comprising a baffle frame with a plurality of parallel tube supportmembers secured to the baffle frame in a plane substantiallyperpendicular to the longitudinal axis, each tube support memberextending in a first orientation in alternating x-tube lanes; a firstset of tube support stakes inserted in the tube bundle adjacent to andspaced from the first tube support cage substantially parallel to andoffset from at least some of the tube support members; a second tubesupport cage comprising a baffle frame with a plurality of parallel tubesupport members secured to the baffle frame in a plane substantiallyperpendicular to the longitudinal axis, each tube support memberextending in a second orientation at an angle to the first orientationin alternating y-tube lanes; a second set of tube support stakesinserted in the tube bundle adjacent to and spaced from the second tubesupport cage substantially parallel to and offset from at least some ofthe tube support members; a third tube support cage comprising a baffleframe with a plurality of parallel tube support members secured to thebaffle frame in a plane substantially perpendicular to the longitudinalaxis, each tube support member extending in the first orientation inalternating x-tube lanes that are offset by one lane from the first tubesupport cage; a third set of tube support stakes inserted in the tubebundle adjacent to and spaced from the third tube support cagesubstantially parallel to and offset from at least some of the tubesupport members; a fourth tube support cage comprising a baffle framewith a plurality of parallel tube support members secured to the baffleframe in a plane substantially perpendicular to the longitudinal axis,each tube support member extending in the second orientation inalternating y-tube lanes that are offset by one lane from the secondtube support cage; and a fourth set of tube support stakes inserted inthe tube bundle adjacent to and spaced from the fourth tube support cagesubstantially parallel to and offset from at least some of the tubesupport members, wherein the first, second, third and fourth tubesupport cages form a set that together defines a grid of tube supportmembers disposed in each x-tube lane and each y-tube lane, and each tubesupport cage is spaced apart at least a distance of 300 mm measuredalong the longitudinal axis, and wherein the tube support stakes biasthe tubes against adjacent tube support members.
 22. The tube bundledevice of claim 21, wherein the tube support members have a thicknessthat is between 90-98% of the width of an x-tube lane or a y-tube lane,thus defining free space between each tube and an adjacent tube supportmember.
 23. The tube bundle device of claim 21, wherein each tubesupport cage is spaced apart a distance of at least 600 mm measuredalong the longitudinal axis.
 24. The tube bundle device of claim 21,wherein each tube support cage is spaced apart a distance of at least1200 mm measured along the longitudinal axis.
 25. The tube bundle deviceof claim 21, wherein the tube support stakes have a plurality of spacedprojections, the projections forming a seat for an adjacent tube. 26.The tube bundle device according to claim 25, wherein the spacedprojections are one of spaced dimples and spaced corrugations.
 27. Thetube bundle device of claim 21, wherein the tube support stakes have aplurality of spaced saddles, each saddle forming a seat for an adjacenttube.
 28. The tube bundle device of claim 21, wherein some of the tubesupport stakes have a plurality of spaced dimples and some of the tubesupport stakes have a plurality of spaced saddles, the dimples andsaddles forming seats for adjacent tubes.
 29. The tube bundle device ofclaim 21, wherein at least some of the tube support stakes have acombination of dimples and saddles that form seats for adjacent tubes.30. The tube bundle device of claim 21, wherein each tube support memberis a flat bar.
 31. The tube bundle device of claim 21, wherein eachbaffle frame is formed of a plate with a central cut-out window.
 32. Thetube bundle device of claim 21, further comprising a shell and atubesheet connected to the shell that supports the tube bundle.
 33. Thetube bundle device of claim 21, wherein the tube bundle having a firstend forming an entrance region and a second end forming an exit region,wherein the tube bundle device further comprising at least oneadditional tube support stake inserted into the tube bundle adjacent oneof the first end and the second end.
 34. A heat exchanger having a tubebundle for transporting fluids for heat exchange, comprising: tubesarranged parallel to one another and defining a tube bundle with alongitudinal axis, wherein the tubes are arranged in rows and columnswith an x-tube lane separating adjacent rows and a y-tube laneseparating adjacent columns; a set of four tube support cages, each tubesupport cage comprising a baffle frame with a plurality of parallel tubesupport bars secured to the baffle frame in a plane substantiallyperpendicular to the longitudinal axis, wherein the set of four tubesupport cages are axially spaced along the longitudinal axis such thatthe tube support bars of two tube support cages extend in a firstorientation in alternating x-tube lanes and the tube support bars of theother two tube support cages extend in a second orientation at an angleto the first orientation in alternating y-tube lanes; and at least oneset of tube support stakes inserted in the tube bundle adjacent to andspaced from at least one of the tube support cages substantiallyparallel to and offset from at least some of the tube support members ofthe adjacent tube support cage in a woven configuration, wherein thetube support stakes are formed with seats to support the tubes, whereinthe set of four tube support cages together define a grid of tubesupport bars disposed in each x-tube lane and each y-tube lane, and eachtube support cage is spaced apart from another tube support cage in theset at least a distance of 300 mm measured along the longitudinal axis,wherein the tube support bars have a thickness that is at most 98% ofthe width of an x-tube lane or a y-tube lane, thus defining free spacebetween each tube and an adjacent tube support bar, and wherein the tubesupport stakes support the tubes in the seats and bias the tubes againstadjacent tube support bars.